Adaptive protection for recloser control

ABSTRACT

A recloser is adaptively controlled so that it will operate in a manner responsive to prevailing conditions such as time of day, day of week, and/or load current. A protection setting group is stored in a memory accessible by the recloser controller, and contains a set of instructions for controlling the recloser based on the prevailing conditions. The prevailing conditions are continuously monitored, and the control of the recloser is based on the prevailing conditions and the protection setting group.

FIELD OF THE INVENTION

[0001] The present invention relates in general to the field ofelectrical power distribution systems. More particularly, the presentinvention relates to reclosers.

BACKGROUND OF THE INVENTION

[0002] A common problem in almost any electrical power distributionsystem is a momentary disruption of electrical service, such as might becaused by a momentary short circuit. For example, power lines strungbetween poles could swing under wind loading, momentarily touching eachother or a grounded conductor. Things may fall across exposed wires,arcing could occur, or other transitory events could cause momentarypower line short circuits or current surges that could burn out a fuseor trip a recloser. Most of these faults are self-correcting and do notrequire permanent fuse or recloser protection because they terminatequickly. If a fuse should burn out or a recloser should trip, the powerline would be open and customers would be deprived of their electricalpower. Service calls to replace fuses or reset reclosers would then berequired. thus escalating the utility's costs.

[0003] A recloser is a fault-interrupting device used to sense current,voltage, and/or frequency and isolate faulted portions of distributionfeeders. A recloser control device operates a recloser. which can be anelectronic controller. Reclosers are inserted into power lines toprotect a power distribution system.

[0004] More particularly, reclosers are electromechanical devices,similar to circuit breakers. Reclosers are distributed at one or morelocations along a power line, typically upline from a fuse. When therecloser controller detects a fault condition, the recloser will beginto timeout. In other words, the recloser controller will initiate a tripto open the recloser if the fault condition has not cleared itselfduring a fixed time interval, where the time interval is a function ofcurrent. Then, after a time delay, as the name suggests, the recloserwill close, and if the fault condition has been cleared, power serviceis restored. If, however, the fault condition has not been cleared, therecloser controller will again trip open the recloser after a secondfixed time interval. If, after a predetermined number of recloseoperations, the fault condition has not been cleared, the reclosercontroller will permanently lockout the recloser (i.e., permanently openthe circuit). The circuit then remains open until the system is repairedand/or the fault condition is eliminated.

[0005] Thus, one primary function of a recloser is to save fuses. Ingeneral, this is done by sensing the peak value of the current conductedand interrupting its flow by opening or tripping a recloser before afuse blows. After a time delay, the recloser closes, thereby restoringpower to the system where it remains closed until the next fault issensed.

[0006] The rate at which a fuse will blow and interrupt current is afunction of the thermal heating of the fusible element. The rate ofthermal heating is proportional to the power generated by the fault andeach fuse has a time current characteristic, which describes the timeinterval required to interrupt the fault current. The time interval isgenerally approximately inversely proportional to the value of the rootmean square of the fault current. It is desirable to coordinate therecloser with the fuses to be saved to insure that the recloser in factinterrupts temporary fault currents before the fuses to be protected areblown. This is generally done by approximating the root mean squarevalue of the fault current by sensing its peak value.

[0007] It must also be recognized that not all faults, which occur on apower distribution line. are temporary, such as those caused by a treebranch momentarily falling against the line. Some faults are of a morepermanent nature such as those caused by a storm where the entire polestructure has fallen to the ground. As a consequence, reclosers arebuilt so that they will only trip a limited number of times within ashort duration before locking open. Were this not done, a recloser wouldcycle until failure and many of the fuses to be protected would blowanyway.

[0008] At some magnitude of fault current it is desirable to have therecloser open immediately to protect the line rather than following aninverse time current characteristic. At intermediate levels it may bedesirable from the power distribution standpoint to allow the faultcurrent to flow for a limited period to allow the fault to burn itselfopen or blow the fuse. Many reclosers have alternate inverse timecurrent characteristics, which achieve this goal. Typically, a recloserwill allow two shots or trip operations to follow a fast time currentcharacteristic and two additional shots along a somewhat slower timecurrent characteristic before locking open or out.

[0009] Conventional reclosers for three-phase systems open all threephases at the same time upon detection of a fault on any one phase.Other three-phase systems implement three single-phase reclosers, one oneach phase. In these systems, each single-phase recloser isindependently controlled. This is costly and does not allow for thephases to be responsive to one another.

[0010] Thus, in a typical configuration, for a fault, the recloser willopen to clear the fault. Note that for any fault, e.g.single-phase-to-ground faults, phase-to-phase faults,phase-to-phase-to-ground faults, and three-phase faults, a typicalrecloser will open all three phases. For distribution feeders, openingall three phases for a single-phase fault will result in more customerslosing power than necessary. However, if an electric utility were toemploy traditional single-phase recloser protection on theirdistribution system, it would be implemented with three independentsingle-phase mechanical reclosers—one for each phase. This provides aper phase approach to single-phase faults but if there is an evolvingfault, such as, for example, two or more phases are faulted, then thetripping and subsequent reclosing is always done single-phase. Totallyindependent single-phase reclosers can also be involved in a racecondition. For phase-to-phase faults, if one phase was to operate morequickly than the other does, the recloser may not correctly isolate thesecond faulted phase.

[0011] The recloser controller provides the intelligence that enables arecloser to sense overcurrent faults, select timing operations, time thetripping and reclosing functions, and lockout. The hydraulic unit—anintegral part of the recloser is used in all single-phase reclosers andhas a smaller rating of three-phase reclosers. The electronic controlleris generally used in the single-phase reclosers and in higher ratings ofthree-phase reclosers. Such devices, however, should be appropriatelyprogrammed to coordinate in a predefined manner to endure that the powerdistribution systems respond to line faults in accordance withexpectations.

[0012] Generally, when automatic circuit reclosers are used inconjunction with fuses, they are configured in a variety of modes. Forexample, the recloser or reclosing breaker may be configured for a fusesaving or fuse clearing mode. In the fuse saving mode, the automaticrecloser or reclosing breaker operates faster than a fuse, trying toclear a momentary fault. If the fault is still present, the automaticcircuit recloser operates more slowly than the fuse, enabling the fuseto blow and clear the fault. In the fuse-clearing mode, the automaticrecloser is set so that for a fault beyond any fuse in series with therecloser, the fault shall be cleared by the fuse without causing therecloser to operate.

[0013] There are microprocessor-based recloser controllers which arecapable of detecting fault conditions, and, in response, capable oftiming out a corresponding recloser. However, these prior designs arenot adaptive. Instead, fault detection in these prior designs is afunction of some absolute (i.e., a fixed) preprogrammed current level,such that gradual changes in load current due to normal, daily and/orseasonal fluctuations are not taken into consideration. Therefore,service may be unnecessarily interrupted when the current fluctuationdoes not pose a threat to the system. Moreover, fault detection schemesbased on an absolute current level may not always detect remote faults(i.e., faults that occur along a distal portion of a power line withrespect to the position of the recloser).

[0014] It is thus desirable to provide recloser control that canovercome the problems of the prior art. In this way, an electric utilitycan adaptively set a recloser to function in a certain manner, such asfuse saving, fuse clearing, single-phase, or three-phase, based onprevailing conditions, such as time of day, day of week, month, or loadcurrent, for example.

SUMMARY OF THE INVENTION

[0015] The present invention is directed to recloser operation that isresponsive to a particular protection setting group. Depending on theprevailing conditions, such as the time of day or the load current, therecloser functions in a certain manner, such as single-phase or in afuse saving mode.

[0016] According to one embodiment within the scope of the presentinvention, a method for controlling a recloser for an electrical powerline comprises determining a protection setting group, the protectionsetting group having at least one associated feature; determining apresent condition of the at least one associated feature; determining abehavior function for the recloser based on the protection setting groupand the present condition; and implementing the behavior function forthe recloser, thereby controlling the recloser responsive to thebehavior function.

[0017] According to aspects of the invention, the present condition iscontinuously monitored, and the behavior function is changed responsiveto the monitoring. The monitoring can take place at predetermined timesor events, such as predetermined intervals of time.

[0018] According to another embodiment within the scope of theinvention, a recloser control system for an electrical power linecomprises a recloser, a memory comprising a protection setting grouphaving at least one behavior function with an associated feature, and arecloser controller coupled to the recloser and the memory forcontrolling the recloser responsive to one of the at least one behaviorfunctions in the protection setting group.

[0019] The foregoing and other aspects of the present invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a simplified schematic diagram of a system in which thepresent invention may be embodied;

[0021]FIG. 2 is a simplified schematic diagram of an exemplaryprotection setting group in accordance with the present invention;

[0022]FIG. 3 is a simplified schematic diagram of another exemplaryprotection setting group in accordance with the present invention; and

[0023]FIG. 4 is a flow chart of an exemplary method of operation inaccordance with the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS AND BEST MODE

[0024] The present invention is directed to systems and methods foradaptively controlling a recloser so that it will operate in a mannerresponsive to prevailing conditions such as time or load current.

[0025] Electrical transmission lines and power generation equipment mustbe protected against insulation faults and consequent short circuits,which could cause a collapse of the power system, serious and expensiveequipment damage, and personal injury. Further, extensive power outagesmay cause angst among consumers that expect reliable and trustworthyutility service. It is the function of the fault protection devices suchas fuses and protective relays to assist in the isolation of line faultsand initiate isolation by tripping reclosers. In addition, powerdistribution operators employ automatic power restoration components toautomatically bring power distribution systems back on-line in the eventof a protection fault or other system malfunction.

[0026] Automatic recloser devices are used in electrical distributionsystems to protect high voltage power lines. Such devices are usuallymounted to the poles or towers that suspend power lines above theground. However, use with below ground systems is also known. Therecloser device is used to minimize power distribution interruptionscaused by transients or faults.

[0027] Typically, during a system disturbance, large increases incurrent, i.e., faults, will occur. Sensing a current increase, therecloser will open thereby cutting off current flow in order to protectdistribution system components and other equipment connected to thedistribution system. Since many fault conditions are temporary, therecloser is designed to close after a short time delay, therebyestablishing normal current flow. For example, during a thunderstorm, iflightning were to strike the distribution system, the power to one'shome may be disrupted for a few seconds causing lights and appliances toturn OFF (recloser opening), then ON (recloser closing). Once therecloser closes, if it senses the continued presence of increasedcurrent, (e.g. fault current rather than load current), it will againopen. Such cycling between open and closed may occur three times beforethe recloser remains open.

[0028] when used in conjunction with other protection devices, such as afuse or protective relay an automatic power restoration device mayoperate in two modes, fuse saving or fuse clearing. In the fuse savingmode, the automatic power restoration device operates faster than acooperating fuse, trying to clear a momentary fault. In the event thefault is still present after the restoration device's attempts torestore the system, the automatic power restoration device operates moreslowly than the fuse, allowing the fuse to clear the fault. In the fuseclearing mode, the automatic power restoration device is configured sothat a fault occurring beyond any fuse that is connected in series withsuch fault is cleared by the fuse without causing the recloser tooperate.

[0029] A simplified schematic diagram of a system in which the presentinvention may be embodied is shown in FIG. 1. A recloser 10 is a switchthat opens and closes a power line 5 (e.g., between a substation and aload), and which is operated by a recloser control device 20 such as anelectronic controller. It should be understood that the term “recloser”covers various combinations of reclosers, sectionalizers, circuitbreakers and the like, which may also be used within the scope of thisinvention. The power line 5 is a three-phase power line. The recloser 10comprises three poles 15. Each pole 15 is connected to an associatedwire on the power line 5, thereby being energized by an associatedphase.

[0030] The basic components of an automatic recloser 10 are a high-speedcircuit breaker, overcurrent protection, trip logic, and automaticclosing logic with an operation counter. When an overcurrent ofsufficient magnitude (i.e., greater than a predetermined amount ofcurrent) flows through the recloser 10, the tripping action is initiatedand a circuit interrupting contact within the pole 15 opens with anoperation counter advancing one count. After a preset time delay, therecloser contacts are automatically closed, thereby re-energizing theline 5. If the fault persists, this tripping and reclosing sequence isrepeated a predetermined number of times, as set by the controller 20,until a lockout function is initiated. If the fault was transient andcleared during any period when the recloser 10 was open, then therecloser 20 will remain closed after a short time delay reset to itsoriginal condition ready for the next operation.

[0031] An exemplary recloser for use with the present invention is theVR-3S recloser manufactured and distributed by ABB Power T&D Company,Inc., Raleigh, N.C. Magnetic actuators open and close the recloser'smain contacts.

[0032] The recloser 10 is controlled by a microprocessor-basedcontroller 20 that contains software. There are two basic design areasthat make up a microprocessor-based controller 20. The physicalelements, such as integrated circuits, resistors, capacitors, displays,switches, and so forth, are called “hardware”. Once constructed, theyare not readily changeable. The second basic design area in themicrocomputer includes computer programs and documentation. Theseelements are called “software” since they are readily changeable.

[0033] A microcomputer based on a microprocessor and associated memoriesand interfacing components is used in the recloser controller 20 toprocess input signals in a manner appropriate for recloser control. Themicroprocessor performs the various arithmetic and logic functions ofthe control. In particular, the required logic circuits as well ascapabilities for servicing are typically included.

[0034] A power supply is typically provided in a recloser control systemand provides power to other components of the control system andincludes power storage means to supply power when the protected linesare interrupted. A secondary overcurrent trip circuit in the controlfunctions independently of the microcomputer when the microcomputer isdisabled to effect a trip operation of the recloser. A protective inputnetwork protects the controllers low power devices from the hostileenvironment of the power distribution system and scaling means are usedto allow the microcomputer and associated circuitry to function withmore precision in the range of input signal magnitudes where precisionis desirable and to allow the control to function with a limited numberof components over a wide range of input signals.

[0035] Storage or memory 30 is provided for temporarily and/orpermanently storing data. In a recloser 10, for example, this data wouldinclude line current magnitudes and command information such as multipletime-current characteristic curves and protection setting groups, asfurther described below. The memory can be random access memory (RAM) orread only memory (ROM) or any other type of memory. ROM is preferablyelectrically programmable for easy modification and is used for storingprogramming information. The storage 30 can be internal to thecontroller 20, as shown, or be located external to the controller 20.

[0036] The front panel of a recloser controller 20 may include a displayfor displaying information, A keyboard or other input device may be usedfor entering information. Indicator lamps provide status informationsuch as recloser open, recloser closed, control lock out, above minimumtrip, malfunction and lock in.

[0037] Through the use of the switches and keyboard mentioned above, theoperations of the device can be controlled by command information.Typical command information for a recloser controller includes firsttime current characteristics for phase and ground currents which usuallyresult in the more rapid tripping of the recloser 10, and second timecurrent characteristics for phase and ground currents which usuallyresult in the recloser 10 remaining closed longer under faultconditions. Other command information includes minimum trip levels forphase and ground currents which in a recloser controller begins thetiming process in accordance with the time current characteristic,number of shots to lock out under phase and ground faults, and number oftimes which a given time current characteristic will be followed.Further command information may include a reset time interval whichdetermines the duration which a counter recording the shot number willretain that information under non-fault conditions, and multiple recloseintervals which determine the time that the recloser 10 will remainopen. Additional command information may include a high current constanttime feature which allows the recloser 10 to remain closed only for afixed duration under certain magnitudes of fault currents. Thus, ifthere is a fault, the line 5 is opened for a short period of time. At anend of a given time period following the opening of the line 5, therecloser 10 closes the line 5. If the abnormal condition persists, therecloser 10 again opens and closes the line 5.

[0038] The command information in accordance with the present inventioncan include a plurality of independent protection settings groups. Theprotection setting group can be programmed by a technician or by thecustomer, either when the system is on-line or off-line. A protectionsetting group is an instruction set for controlling a recloser based oncertain conditions. An exemplary protection setting group is shown inFIG. 2. Here, the protection setting group is based on time of day andday of week. A fuse-clearing mode is enabled for a particular time andday (e.g., during business hours, Monday through Friday) and a fusesaving mode is enabled for the remaining times (e.g., during weekendsand after business hours). In this manner, the quality of supply isoptimized for a majority of customers during business hours, Mondaythrough Friday, and operating expenditures are minimized when thequality of the supply is not as critical (during weekends and afterbusiness hours).

[0039] Another exemplary protection setting group is shown in FIG. 3.Here, the recloser is set to operate in one phase (single-phase) mode orthree-phase mode depending on the month of the year. Single-phaseoperation is implemented from October through March, and three-phaseoperation is implemented from April through September. In this manner,for example, in a rural area, irrigation may take place for severalmonths of the year, in which three-phase protection is desired toadequately protect pump motors. During the remaining months, it isdesirable to have one phase protection because active loads aresingle-phase in nature and it is desirable to minimize the effects ofoutages due to faults. Thus, a clock and calendar can be used to controlthe operation of the recloser as single-phase or three-phase operation,and/or fuse clearing mode or fuse saving mode.

[0040] Another exemplary protection setting group can be based on theload current. Based on the load current, different features are enabled,such as fuse saving or fuse clearing protection, and single-phase orthree-phase operation. In this manner, protection can be established tobehave differently to a given fault based on which protection settinggroup is active, based on the prevailing conditions.

[0041] It should be understood any of a number of microprocessors couldbe used to the same effect described above. Each manufacturer's familyrequires that the peculiarities of their devices be satisfied and in themicrocomputer portion of the recloser controller 20, and it would beimpossible to go into sufficient detail to describe the functioningcontrol and be sufficiently general to adequately describe the use ofalternative devices. One skilled in the art could readily amplify andmodify the description given to make them applicable to the devices ofother manufacturers by reading the normal technical literature providedby the manufacturer of another device. Moreover, it would be extremelyconfusing to attempt to describe all the minor details contained withinthe software and only the more general software modules and programs aredescribed since one skilled in the art could readily flesh out theskeleton provided.

[0042] An exemplary control unit is the PCD2000 power control devicemanufactured and distributed by ABB Power T&D Company, Inc., Raleigh,N.C. The control device can provide an interface for remotecommunication with SCADA systems using MODBUS RTU, MODBUS ASCII, and DNP3.0 protocols. The controller can be programmed to implement otherprotocols. Ports are available for external links through a radio,modem, or direct fiber optic communications, for example.

[0043]FIG. 4 is a flow chart of an exemplary method of operation inaccordance with the present invention. During power delivery, therecloser 10 monitors the power line 5. At step 100, the setting group isdetermined, selected, or otherwise set. The setting group can beretrieved from a storage area 30 (e.g., a memory within, or coupled to,the recloser controller 20). A plurality of setting groups (related orunrelated) can be stored in the storage area 30, and a technician orcustomer can choose the desired setting group while the system ison-line or off-line.

[0044] After the setting group has been determined, the present orprevailing conditions of the features associated with the setting groupare determined at step 110. For example, if the setting group of FIG. 2is active, the time of day and day of the week would be determined,because the fuse clearing or fuse saving mode is set dependent on thesetwo parameters. As another example, if the setting group of FIG. 3 isactive, the month of the year is determined, because single-phase orthree-phase operation is set responsive to the month of the year.

[0045] At step 120, the appropriate recloser behavior is determined fromthe protection setting group based on the prevailing conditions. This isperformed by comparing the prevailing conditions step 110 to theconditional entries in the protection setting group step 100, and theentry that matches is implemented, at step 130. Thus, for example, ifthe setting group of FIG. 2 is active, and it is 1:00 pm on a Wednesday,then based on the protection setting group entries, the fuse clearingmode is implemented.

[0046] The present or prevailing conditions are continuously monitored,at step 140, to determine if the recloser behavior should be changed, asdetermined at step 150. If the behavior should change, the new behavioris determined and implemented with processing continuing at step 130. Ifthe behavior should not change, the conditions are monitored, withprocessing continuing at step 140. The prevailing conditions aremonitored at predetermined intervals (of time, for example) or at otherevents, which can be programmed by a technician or customer.

[0047] Thus, for example, if the setting group of FIG. 2 is active, whenthe time changes from 5:00 pm to 5:01 pm, on a Wednesday, the modechanges from fuse clearing to fuse saving. The fuse saving mode isimplemented until 8:00 am on Thursday, at which time the mode changes tofuse clearing.

[0048] The invention may be embodied in the form of appropriate computersoftware or in the form of appropriate hardware or a combination ofappropriate hardware and software without departing from the spirit andscope of the present invention. Further details regarding such hardwareand/or software should be apparent to the relevant general public.Accordingly, further descriptions of such hardware and/or softwareherein are not believed to be necessary.

[0049] Although illustrated and described herein with reference tocertain specific embodiments, the present invention is nevertheless notintended to be limited to the details shown. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the invention.

What is claimed:
 1. A method for controlling a recloser for anelectrical power line, comprising: determining a protection settinggroup, the protection setting group having at least one associatedfeature; determining a present condition of the at least one associatedfeature; determining a behavior function for the recloser based on theprotection setting group and the present condition; and implementing thebehavior function for the recloser, thereby controlling the recloserresponsive to the behavior function.
 2. The method according to claim 1,further comprising continuously monitoring the present condition andchanging the behavior function responsive to the monitoring.
 3. Themethod according to claim 2, wherein the monitoring the presentcondition comprises monitoring at predetermined intervals.
 4. The methodaccording to claim 1, wherein the at least one associated featurecomprises one of time of day, day of week, and month of year.
 5. Themethod according to claim 1, wherein the at least one associated featurecomprises load current.
 6. The method according to claim 1, wherein thebehavior function comprises one of fuse saving mode and fuse clearingmode.
 7. The method according to claim 1, wherein the behavior functioncomprises one of single-phase operation and three-phase operation.
 8. Arecloser control system for an electrical power line, comprising: arecloser; a memory comprising a protection setting group having at leastone behavior function with an associated feature; and a reclosercontroller coupled to the recloser and the memory for controlling therecloser responsive to one of the at least one behavior functions in theprotection setting group.
 9. The recloser control system according toclaim 8, wherein the recloser controller monitors a present condition ofeach associated feature of each behavior function in the protectionsetting group, and determines the behavior function based on the presentcondition.
 10. The recloser control system according to claim 8, whereinthe recloser controller comprises the memory.
 11. The recloser controlsystem according to claim 8, wherein the one associated featurecomprises one of time of day, day of week, and month of year.
 12. Therecloser control system according to claim 8, wherein the associatedfeature comprises load current.
 13. The recloser control systemaccording to claim 8, wherein the at least one behavior functioncomprises one of fuse saving mode and fuse clearing mode.
 14. Therecloser control system according to claim 8, wherein the at least onebehavior function comprises one of single-phase operation andthree-phase operation.
 15. A computer-readable medium havingcomputer-executable instructions for performing steps comprising:determining a protection setting group for a recloser operating on anelectrical power line, the protection setting group having at least oneassociated feature; determining a present condition of the at least oneassociated feature; determining a behavior function for the recloserbased on the protection setting group and the present condition; andimplementing the behavior function for the recloser, thereby controllingthe recloser responsive to the behavior function.
 16. Thecomputer-readable medium according to claim 15, further comprisingcomputer-executable instructions for continuously monitoring the presentcondition and changing the behavior function responsive to themonitoring.
 17. The computer-readable medium according to claim 16,wherein monitoring the present condition comprises monitoring atpredetermined intervals.
 18. The computer-readable medium according toclaim 15, wherein the at least one associated feature comprises one oftime of day, day of week, month of year, and load current.
 19. Thecomputer-readable medium according to claim 15, wherein the behaviorfunction comprises one of fuse saving mode and fuse clearing mode. 20.The computer-readable medium according to claim 15, wherein the behaviorfunction comprises one of single-phase operation and three-phaseoperation.